What is the use of __threshold__ in Python?

I was going through some Python automation scripts and I saw the开发者_如何学JAVA new (for me) keyword of ___threshold__ = 0.6. What it indicate? What it is used for?

There are only three hits for python "__threshold__" in Google. This doesn't have any special meaning in Python, it's just an identifier someone chose to use. __this_format__ is only supposed to be used by built-in names, to prevent confusion like this.